The development of the laser and related light stimulative technology has generated a significant interest on the part of investigators in that branch of interferometry known as holography. In its underlying concept, holography generally considers that the scattering pattern of light from an object is a transform, or coded record, of the features of that object. Where such a scattering pattern is stored, for example, photographically, an image of the object should be reconstructable. Prior to the availability of an intense coherent light source, a required recordation of such patterns proved most difficult. However, with the availability of the laser as an intense coherent light source and with an innovation wherein the scattering pattern was combined to interfere with a reference beam of coherent light, a photographic wave-front reconstruction was realized. With the interference of reference and reflective subject beams, resultant interference fringes exhibited a recordable contrast representing a measure of amplitude of the subject beam and the position of these fringes represented a recordable measure of phase of the subject beam. Where a photograph of such an interference pattern is illuminated with a laser beam identical with the original reference beam, diffracted light from the photograph will have the same amplitude and phase characteristics as the original beam from the subject.
The most interesting aspect of the holographic reconstruction resides in the very detailed and three-dimensional nature of a resultant image. Additionally, holograms have been found useful in the evaluation of stress exerted upon structural components. The three-dimensional resolution of motion picture holograms has been found helpful in studying microscopic life such as plankton. Holographically produced lenses have found use in aircraft windshield displays, while holographic scanners are used in retail price code scanning assemblies.
For each of the above and other applications, the holographic information storage is photographic in nature and, thus, somewhat limiting in application. However, the relatively large amount of imaging data available in a holographic image record should find extensive application within a broad range of developing technologies. In particular, a significant extension of holographic applications will occur where such records become the subject of electronic storage. Further, where electronic wave-front reconstruction is available, an advantageous holographic imaging and transmission in real time may be achieved.
Recently a system has been devised wherein holographic data may be generated, recorded and/or transmitted as electrical signals for utilization in a broad variety of applications. The system employs an imaging device formed having spaced, mutually orthogonally disposed transparent, planar electrode arrays. Between these arrays there is disposed a dipolar fluid which normally is opaque, but which becomes light transmissive in the presence of an applied electric field. Thus, a matrix of spaced electrode crossing locations is developed which is utilized to generate image pixel positions. A control is electrically coupled with the two electrode arrays for sampling this matrix of locations by generating an electrical field of predetermined value between sequentially selected pairs of electrodes within the arrays. By positioning a light responsive detecting arrangement with the device, an electrical output signal is generated which corresponds with the light intensity of the interference pattern imposed upon the device at any given sample matrix location. The spatial density of the pixel array is quite significant, pixel diameters of about 2 microns which are spaced on 4 micron centers being contemplated.
Essentially the same form of imaging device may be utilized in a reconstruction mode wherein an electrical signal train developed in a construction mode is utilized for purposes of carrying out scanning of the pixel matrix to define pixel diameters corresponding with image intensity. The entire system is described in U.S. Pat. No. 4,484,219 by Ronald L. Kirk, entitled "Electrically Generated Holography", issued Nov. 20, 1984.
Because of the relatively high spatial frequency of the pixel format of the imaging devices, it has been observed that some "cross-talk" or field interference occurs in conjunction with those pixel locations which are adjacent an address pixel location. Further, the form of pixel which is generated has been observed to occur not necessarily as a transparent cylindrical form but, as a grouping of four transparent areas arranged in quadrature about the center position of a given pixel. In view of the large spatial frequency of pixels, some form of scan updating is desirable, particularly in a reconstruction mode of operation. However, typical approaches for scanning update as are encountered in videotechnologies and the like are not particularly desirable for the instant utilization. This stems from the earlier-noted high spatial frequency of the pixel locations.
When the instant devices are utilized in conjunction with systems generating images for human vision, the control circuitry providing for their operation also must be capable of accommodating the noted relatively high spatial frequency of pixel format in a manner developing a desired frame rate. Where frame rates fall below, for example, about 30 frames per second, undesirable flicker phenomena may be observable in any viewed image. Achieving such frame rates utilizing conventinal point-to-point scanning techniques will be found to be generally ineffective inasmuch as frame rates necessarily are dependent upon the rise time requirements of any given pixel. Thus, notwithstanding the very high scan rates available with current electronic scanning approaches, the development of adequate frame rates for devices of the instant character becomes an elusive task.
The above-described device or structure as initially developed for applications with holographic systems has been found to exhibit advantageous utility in a broadened range of optical processing applications wherein it functions generally as a spatial light modulator. Current spatial light modulation devices suffer a variety of operational deficiencies, for example, exhibiting insufficient contrast ratios and lack of resolution. Recourse to the instant technology with respect to optical processing requirements otherwise looking to spatial light modulation techniques promises considerable operational enhancements.